Electrochemical storage devices, such as batteries, can be classified into either primary or secondary batteries. Primary batteries are not designed to be recharged and are not reusable after they have been fully discharged. Secondary batteries, however, are rechargeable after they have been fully discharged. The demand for rechargeable or secondary batteries of high energy density and specific energy has, however, increased with the increasing demand for portable electronic equipment, e.g., cellular phones and laptop computers.
Among the commercially available portable rechargeable battery chemistries, Li-ion batteries provide the highest energy densities. A typical Li-ion cell consists of a lithiated cobalt oxide, lithiated nickel oxide or lithiated manganese oxide based composite cathode, a carbon-based anode, and a lithium ion containing liquid electrolyte. A modification of the Li-ion battery is the lithium-polymer battery in which a polymer or gel electrolyte, e.g., a poly(ethylene glycol) (PEG) electrolyte containing lithium salt, is used in place of a liquid electrolyte. Lithium polymer electrolytes are the electrolyte of choice over Li-ion containing liquid electrolyte in portable electronic applications because the lithium polymer battery can be processed into a thin sheet whereas Li-ion batteries require a container for holding the liquid electrolyte.
A disadvantage of the polymer-gel electrolytes currently used in Li-ion batteries is that they exhibit transference numbers on the order of about 0.2-0.4, much less than unity. By optimizing the transference number of the electrolyte, the formation of charge gradients in an electrochemical cell can be reduced, leading to a reduction in energy losses and increased efficiency. Polymeric lithium single ion conductors, defined as polymers in which anionic moieties are fixed in the polymer backbone with free or loosely bound lithium ions, are expected to produce transference numbers closer to unity by virtue of their structure in which lithium ions are free to move along the polymer backbone. However, reports of the successful synthesis of such materials are rare.
What is needed are new monomers that can be polymerized to produce conductive polymers suitable for use in applications such as lithium ion batteries.